1. Field of the Invention
This invention relates generally to chip type semiconductor light emitting devices and, more particularly, to a chip type semiconductor light emitting device having a semiconductor light emitting chip connected to an electrode and molded together with part of the electrode by a resin, such as epoxy.
2. Description of the Prior Art
There is known a structure shown in FIG. 7 as a chip type semiconductor light emitting device of this kind. FIG. 7 is a perspective view showing, by partly seeing through, a chip type semiconductor light emitting device 1. In FIG. 7, a pair of electrodes 3, 4 are formed, and the electrode 4 is formed with a pad 4b. Reference characters 3a, 4a respectively represent terminal portions of the pair of electrodes 3, 4.
A semiconductor light emitting chip (hereinafter abbreviated as "LED chip") 5 has, on its top surface, an electrode 5a electrically connected by wire-bonding to the electrode 3 through using a metal wire 6. Also, the LED chip 5 is bonded on the pad 4b of the electrode 4 through a conductive paste. The LED chip 5 at its backside electrode is electrically connected to the electrode 4. The LED 5 and the metal wire 6 are encapsulated together by a mold 7 using a translucent synthetic resin. Meanwhile, each electrode 3, 4 has a terminal portion 3a, 4a extending outside the mold 7 to a backside of the substrate through a side surface thereof.
In this manner, in the example of FIG. 7 the LED chip 5 and the metal wire 6 are encapsulated in a state that the mold 7 at its end faces is partly jointed to the terminal portions 3a, 4a of the electrodes 3, 4. The chip type semiconductor light emitting device 1 is mounted with an backside of the substrate 2 positioned down on a surface of a circuit board, and subjected to a reflow process so that the terminal portions 3a, 4a of the electrodes 3, 4 are brought into electrical connection through solder onto a circuit pattern of the circuit board.
FIG. 8 is a sectional view showing, by magnification, a structure of the electrode and terminal portion formed on the substrate 2. On the substrate 2, a copper (Cu) layer is first formed and then a nickel (Ni) layer and gold (Au) layer are formed on the copper layer by electroplating. Thus, Cu, Ni and Au three conductive layers are formed on the substrate 2.
The Au layer thus formed on the surfaces of the pair of electrodes and terminal portions makes it easy to deposit solder on the terminal portions. Furthermore, where a gold wire is used as a wire-bonding metal wire, preferred electrical connection is provided between the metal wire and the electrode, thus improving the quality of the semiconductor light emitting device 1.
In the case where the semiconductor light emitting device 1 mounted on a circuit board experiences repetition of a reflow process, if the amount of a solder melt is comparatively much, the solder melt may flow along an Au layer on a terminal portion 3a, 4a and intrude at a mold 7 end face toward an electrode 3, 4. FIG. 9 is a perspective view depicting a state that a solder melt 8 flows, as shown by an arrow X, from one terminal portion 3a through a mold 7 end face and intrudes to the electrode 3.
If the solder 8 flows along the Au layer on the surface of the terminal portion 3a, 4a and intrudes through the mold 7 end face to the electrode 3, 4 as shown in FIG. 8, there is a possibility that the metal wire 6 that is wire-bonded to the electrode 3 be broken due to an impact caused by the solder melt 8 or the LED chip 5 be stripped off the pad 4b of the electrode 4. If the metal wire 6 or the semiconductor light emitting chip 5 is damaged due to intrusion of solder 8, a problem results that the semiconductor light emitting device 1 would not operate normally.